Dietary selenium intake and selenoproteins in rat plasma.

Selenium (Se) is vital for animals and humans, as it is an essential component of Se-dependent glutathione peroxidase (GPx), an enzyme that reduces peroxides and protects cells against the damaging effects of oxidation. Se has, however, been found in rat plasma even when the enzymatic activity of GPx is very low, supporting the hypothesis that Se is also bound to other proteic structures. The purpose of this work was partially to purify the selenium-containing proteins in plasma, without denaturation, by isoelectrofocusing. We observed two pH intervals in the plasma where Se-containing proteins concentrated upon focusing: the first, at pH 6.0 +/- 0.2 and with GPx activity, and the second, between pH 4.6 and 5.4, with no enzymatic activity. We can infer therefore that other Se-containing proteins are present at a lower pH than 6, and in particular between 4.6 and 5.4